1. Field of the Invention
The present invention relates to a fuel injection system with a fuel injection pump for an internal combustion engine.
2. Description of the Related Art
In a diesel engine, pressure within the engine cylinder becomes very high at fuel injection time, so that a usual fuel injection system has a fuel injection pump for injecting fuel under pressure into the engine cylinder. The fuel injection pump is usually a positive displacement type and varies the volume of the fuel injected, according to the current engine operating conditions. However, to realize a desired engine operating condition, the required weight of fuel must be injected into the engine cylinder, so that when the density or the bulk modulus of the fuel changes, a desired engine operating condition can not be realized by the above fuel injection system.
The density and the bulk modulus of fuel change corresponding to fuel temperature. Accordingly, in the usual fuel injection system, the volume of fuel injected is corrected corresponding to the fuel temperature. However, fuels sold in a market do not always have the same properties. If fuel resupplied has properties which are largely different from standard properties, it is necessary to detect the properties of the fuel, for example the density or the bulk modulus corresponding to fuel temperature, which affect the weight of fuel injected and to correct the volume of fuel injected according to the new properties.
For this purpose, Japanese Unexamined Patent Publication No. 2-64250 discloses a fuel injection system having correcting means for correcting the volume of the injected fuel, according to fuel properties imputted thereinto.
The above fuel injection system also needs an analyzing device for analyzing the fuel properties. Such an analyzing device is usually large and very expensive. Accordingly, it is very difficult to mount it in a vehicle and thus it is necessary for a driver to analyze the fuel properties at every refueling by using the analyzing device which is installed in a certain place, so that the above fuel injection system is not practical.